The present invention relates to a method and apparatus for controlling a fuel injection valve having a piezoelectric actuator as the valve member, which opens up or closes a connection to a space arranged downstream. An electric actuating element actuates the valve member and a prestressing element prestresses the valve member into a prestressing direction. Furthermore, a sensor element is arranged on the same axis as the valve member and supplies an output signal to a control unit concerning the forces acting upon the valve member.
Such an operation is known from German Patent document DE 101 27 932 A. The sensor element is to be used for determining any engine knocking. The mechanical impulses are converted to electric signals by way of the sensor element. These signals are evaluated by the control device. However, in this case, it should only be possible to detect the pressure via the sensor element only in the inactive phase of the valve (completely open valve or completely closed valve).
There is therefore needed a method and apparatus of the above-mentioned type which allows for reliable control of the fuel injection valve during the entire combustion process.
The present invention achieves this object by providing a method and apparatus for controlling a fuel injection valve, including a piezoelectric actuator as the valve member, which opens up or closes a connection to a space arranged downstream. An electric actuating element actuates the valve member and a prestressing element prestresses the valve member into a prestressing direction. Furthermore, a sensor element is arranged on the same axis as the valve member and supplies an output signal to a control unit concerning the forces acting upon the valve member. The control unit acts upon the actuating element by way of an electric excitation, which has a signal course (phase) at least approximately inverse to the output signal of the sensor element.
The prerequisite of the invention is the special construction of the fuel injection valve. The piezoelectric actuator and the sensor element preferably form a unit. In addition, a prestressing element for the piezoelectric actuator is provided, which prestresses the valve member into a prestressing direction, preferably in a closing manner. The sensor element is on the same axis as the valve member. The output signal will then supply information concerning the forces acting upon the valve member.
These forces are composed of the force exercised by the prestressing element, the force acting upon the piezoelement by electric excitation, the force acting upon the valve by the combustion pressure in the combustion chamber, as well as possible thermal influences. The force acting upon the valve, if correspondingly dimensioned, as a result of the combustion pressure in the combustion chamber, is clearly lower than the force exercised by the prestressing element and the force acting by electric excitation on the piezoelement.
The signal course of the electric power by which the actuating element is acted upon is characteristic of the invention. By means of the signal course, which is at least approximately inverse to the output signal of the sensor element, it is to be achieved that, during the entire opening time, apart from the opening and closing operation, the piezoelectric actuator remains in an at least approximately invariable position.
Within the scope of the invention, a sensor element is preferably used which, like the piezoelectric actuator, has an electrostrictive construction and is preferably arranged together with it on a joint axis with the valve member. The above-mentioned effect can also be obtained if the sensor element is constructed as a magnetostrictive element. As a result, a particularly compact construction is achieved.
Instead of an electrostrictive element, a magnetostrictive element may also be used. In the case of magnetostrictive elements, the geometrical dimensions of a body change under the influence of a magnetic field. The expansion of the body takes place as a function of the magnetic field intensity. The expansion of the body is the larger, the greater the magnetic field intensity. The reversal of this effect is called a magnetoelastic or magnetomechanical effect. In this case, a change of the magnetic induction is caused under the influence of a mechanical tension. In the case of the present invention, this may be used for the application of the magnetostrictive element in the manner of an actuator, as well as in the manner of a sensor. Here, the forces are transmitted by way of the valve member to the magnetostrictive element and can be determined there corresponding to the piezoelectric element on the basis of the occurring change of the magnetic induction. As a result, a magnetostrictive element may also operate in the manner of an actuator, as well as in the manner of a sensor.
In a preferred embodiment of the invention, the actuating elements of several valve members, each equipped with sensor elements, are acted upon by an electric excitation inverse to the output signal of the respective sensor elements by way the control unit in an initial operating phase. Several fuel injection valves in several cylinders are thereby controlled independently of one another and in a mutually identical manner.
A further improvement of the method according to the invention is obtained if, in an operating phase following the initial operating phase, the control unit acts upon the actuating elements of several valve member independently of one another by way of an electric excitation inverse to the output signal of the respective sensor element and the amplitudes of the excitation are selected corresponding to the output signal of a cylinder-selective lambda sensor. This results in a controlling of the fuel injection valves as a function of the output signal of the lambda probe(s) with the possibility of still better control of the fuel injection valves in the sense of an optimizing of the exhaust gas action.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.